Hvci: Bypass

HVCI is a security feature designed to protect the Windows operating system kernel from malicious code execution. It achieves this by utilizing hardware virtualization capabilities, such as those provided by Intel VT-x and AMD-V, to create a secure environment where kernel-mode drivers and code can be executed and monitored. HVCI ensures that any attempt to modify kernel-mode memory regions or execute unauthorized code in kernel mode is blocked, thereby enhancing the system's resistance to certain types of attacks.

HVCI operates by creating a virtualization-based security environment. Here’s a simplified overview of its operation:

In the ever-evolving landscape of Windows security, few defenses have raised the bar as high as Hypervisor-Protected Code Integrity (HVCI) . Introduced with Windows 10 and 1803 (and later made mandatory for certain features in Windows 11), HVCI—often referred to as "Memory Integrity" in the Windows Security UI—is a virtualization-based security (VBS) feature that fundamentally changes how kernel memory is protected.

HVCI ensures that kernel-mode code pages cannot be made writable and executable simultaneously. In simpler terms, it prevents an attacker (or a vulnerable driver) from injecting malicious shellcode into the kernel and executing it. Hvci Bypass

Yet, where defenses rise, offensive security follows. The term "HVCI Bypass" refers to the set of techniques, vulnerabilities, and exploitation strategies designed to circumvent this hypervisor-enforced lockdown. This article delves deep into what HVCI is, why bypassing it is the holy grail of modern kernel exploitation, and the technical methods used to defeat it.

To protect against HVCI bypass attempts, system administrators and users can adopt several strategies:

HVCI also remaps kernel memory. Code sections become read-only at the hypervisor level, and data sections become non-executable. Even if an attacker corrupts a page table entry (PTE), the hypervisor’s shadow page tables will override the request, causing a #GP (General Protection Fault) or a VBS violation. HVCI is a security feature designed to protect

In short, under HVCI, "self-modifying kernel code" becomes impossible.

HVCI does not block signed kernel drivers. It blocks modification of driver code. However, a driver that is already signed and has a vulnerability can be used as a proxy to execute arbitrary code without violating HVCI.

Technique: Call Table Hooking without Modification Instead of writing shellcode, an attacker can: HVCI does not block signed kernel drivers

This is a data-only attack. Since no page becomes executable that wasn’t already executable, and no code is written to a writable page, HVCI is silent.

Real-world: The Netfilter and MalwareFox BYOVD incidents used this to install callbacks into CmpCallbackList (registry callbacks) without ever violating HVCI’s code integrity checks.